Several compositions are widely used in oilfield applications, for example in assisting various operations which are performed for oil recovery from the ground. Examples of such compositions are various working fluids which are pumped to the ground. These fluids have water as carrier and contain dissolved and/or disperesed agents which confer the fluid suitable properties. Examples of such working fluids are drilling muds or drilling fluids, which are used in drilling a drillhole down into the ground where the drilling mud, due to its non-newtonian viscosity behaviour, more precisely its shear-thinning property, is easily pumpable at high shear rates inside the drill due to its low viscosity, but is capable of suspending solid matter (drilling cuttings) and conveying the suspended matter at low shear rates due to its high viscosity up the drill hole. These compositions usually contain polymer dissolved in water at a suitable concentration. Widely used polymers that are used for this purpose as so-called “viscosifiers” or rheology modifying agents include xanthan gum, carboxymethyl cellulose (CMC), poly(acrylamide) (PAM), and polyvinyl alcohol (PVOH).
Other compositions where the viscosity behaviour has important function are hydraulic fracturing compositions, gravel packing compositions and so-called displacement fluids for enhanced oil recovery. All these compositions use some “viscosifier” polymer as the rheology modifying agent.
Other agents that are used in compositions are sealing agents, that is, agents to control lost circulation. These are agents that, when added to fluids pumped to the ground, seal fractures and permeable formations and prevent the loss of the actual working fluid in the ground.
For example U.S. Pat. No. 6,348,436 describes a drilling fluid comprising cellulose nanofibrils which are obtained from cells consisting of at least 80% of primary walls and which are essentially amorphous. The raw material of such nanofibrils are pulp obtained from parenchymal cells, especially from vegetables, for example beetroot pulp. The nanofibrils are charged at the surface with carboxylic acids and with acidic polysaccharides either alone or as a mixture.